The formal investigation is examining Exxon’s longstanding practice of not writing down the value of its oil and gas reserves when prices fall. Exxon is the only major U.S. energy producer that hasn’t taken a write-down or impairment charge since oil prices plunged two years ago. Peers including Chevron Corp. (CVX) have lowered valuations by a collective $50 billion.

But the probe is also homing in on how Exxon calculates the impact to its business from the world’s mounting response to climate change, including what figures the company uses to account for the future costs of complying with regulations to curb greenhouse gases as it evaluates the economic viability of its projects.

About Stocks To Watch

Earnings reports, corporate strategies and analyst insights are all part of what moves stocks, and they’re all covered by the Stocks to Watch blog. We also look at macro issues, investor sentiments and hidden trends that are affecting the market. Stocks to Watch gives you the full picture of the U.S. stock markets, all day long.

The blog is written by Ben Levisohn, a former stock trader who has covered financial markets for the Wall Street Journal, Bloomberg and BusinessWeek.